Prenatal Diagnosis of Fetal Infections

Congenitally Infected Baby

• 1.

  Symptomatic (10%)

  • a.

    50% will have typical features of CMV inclusion disease;

  • b.

    50% will have atypical features.

• 2.

  Asymptomatic 90%

  • a.

    These infants though infected at birth will have no symptoms.

Outcome of Fetal Infection with CMV

The overall risk of damage in fetuses infected as a result of primary maternal infection is about 25%. The earlier the fetus is affected the more severe the disease tends to be. Children with congenital CMV infection following first-trimester infection are more likely to have central nervous system sequelae, especially sensorineural hearing loss.

Symptomatic infected newborns present with at least one of these abnormalities:

• Prematurity.

• Petechiae/purpura, thrombocytopenia, haemolysis.

• Conjugated hyperbilirubinemia/jaundice, hepatosplenomegaly, elevated alanine aminotransferase levels (>80 UI/L).

• Neurological findings (microcephaly, hypotonia, seizures) and increased cerebrospinal fluid proteins.

• Symptomatic CMV inclusion disease (ID) has a mortality rate of around 6%.

Long-term follow-up of the 10% of children who are infected at birth has shown that in 90% of the subjects in this subgroup there will be at least one sequela such as:

• psychomotor delay (70%);

• sensorineural hearing loss (SNHL) (50%);

• ocular abnormalities (mainly chorioretinis) (54%).

Asymptomatic neonates are known to have a better long-term prognosis with 10% to 15% developing sequelae (mainly SNHL) usually within the first 2 years of life.

CMV congenital infection is likely to be the cause of one third of all SNHL in childhood. Antiviral treatment of neonates showing SNHL leads to improved audiologic performance.

Since infection in a healthy mother with normal immunity is frequently asymptomatic, testing for CMV during pregnancy is usually precipitated by the discovery of a fetal marker during a routine ultrasound examination. If CMV infection of the fetus is suspected, the maternal infection status needs to be established initially. Once primary infection or reactivation of maternal CMV is confirmed, prenatal diagnosis can be offered to determine the risk of fetal infection.

Hepatomegaly ( Figure 6-4 )

Fetal liver measurements show quite a wide confidence interval but a 40 mm thickness between the gallbladder and the diaphragm measured either in a parasagittal plane or a frontal plane usually qualifies for hepatomegaly during the second and early third trimester.

Splenomegaly ( Figure 6-5 )

Splenomegaly is measured in a transverse plane of the fetal abdomen limited by the lowest rib, the stomach bubble and the spine. A longest diameter of at least 40 mm during the same gestational window is compatible with splenic enlargement. Splenomegaly may produce a small stomach bubble, shifted somewhat towards the midline, and is often associated with increased amniotic fluid volume resulting from the compression of the stomach by the enlarged spleen and or liver.

Cardiomyopathy

Cardiomyopathy may be seen usually as part of hydrops fetalis related to either anaemia or generalized metabolic failure.

Hyperechogenic Bowel ( Figure 6-3 )

Hyperechogenic bowel is a subjective finding but in this context must be echogenic bowel as bright as bone (EBABAB). EBABAB may be due to meconium ileus. Meconium peritonitis may follow bowel perforation by the virus itself, this feature is often also transient ( Figure 6-6 ).

Hydrops

Hydrops in CMV infection usually presents with moderate ascites, and pleural and pericardial effusions. Skin oedema is usually mild. Hepatosplenomegaly and hyperechogenic bowel are usually present once the fetus is hydropic.

Fetal Brain Involvement

Fetal brain involvement is the main prognostic factor of fetal infection.

The intracranial findings include :

• 1.

  Signs of a ventriculitis:

  • ventriculomegaly;

  • ventricular septations;

  • echogenic ventricular rims ( Figure 6-7 A and B ).

    

• 2.

  Periventricular hyperechogenicity, calcification or porencephaly all of which are a consequence of periventricular leukomalacia.

• These intracranial features are often associated with hyperechogenicity and pseudocysts of the germinal matrix and neuronal migration abnormalities including polymicrogyria ( Figure 6-8 ).

  

• 3.

  Cerebellar abnormalities often present as hyperechoic areas and cerebellar hypoplasia ( Figure 6-9 ).

  

• 4.

  Microcephaly is the end result of brain atrophy and is usually associated with some or all of the above described signs.

Particular attention should be paid to the aspect and size of the pericerebral spaces, where a delay or lack of gyration of the main and secondary fissures and sulci and increased pericerebral spaces will be evident, particularly on coronal views ( Figure 6-10 ).

The ultrasound examination of the fetal brain in infected fetuses should comply with the requirements of a full neurosonogram examining both axial, coronal, sagittal and parasagittal planes searching for sometimes subtle features. However meticulous serial dedicated neurosonograms can be, it is advisable to perform fetal brain MRI in the third trimester of pregnancy since some features, especially migration and gyration abnormalities, will be better seen by MRI.

Growth restriction is described in up to half of symptomatic neonates but also in about a third of asymptomatic ones and this could be due either to placental insufficiency related to infection or else due to severe symptomatic fetal infection.